Update helper function to print nested exception details. (#47437)

Co-authored-by: Connie Yau <conniey@microsoft.com>

Author: azure-sdk-automation[bot]

eng/common/TestResources/TestResources-Helpers.ps1

@@ -349,6 +349,36 @@ function SetDeploymentOutputs(
     return $deploymentEnvironmentVariables, $deploymentOutputs
 }
 
+<#
+   Writes Resource Manager errors which often have nested exceptions.
+   https://learn.microsoft.com/dotnet/api/microsoft.azure.commands.resourcemanager.cmdlets.sdkmodels.psresourcemanagererror
+#>
+function Write-PSResourceManagerError($resourceManagerError, [int]$level, [int]$maxLevel) {
+    if (!$resourceManagerError -or !$resourceManagerError.Message) {
+        return;
+    }
+
+    # Retrieve one or more messages then decode the strings for readability (remove quote escapes, fix link readability, etc.)
+    $parsedMessage = ($resourceManagerError.Message -join "$([System.Environment]::NewLine)$([System.Environment]::NewLine)")
+    $parsedMessage = [System.Net.WebUtility]::UrlDecode($parsedMessage)
+
+    $prefix = " " * ($level * 2) + "-"
+    Write-Host "$prefix $parsedMessage"
+
+    # Limit the level of nested exceptions to prevent overwhelming users with details and infinite recursive calls.
+    if ($level -ge $maxLevel) {
+        if ($resourceManagerError.Details.Count -gt 0) {
+            Write-Host "$prefix ... (additional nested errors not shown)"
+        }
+
+        return;
+    }
+
+    foreach ($detail in $resourceManagerError.Details) {
+        Write-PSResourceManagerError $detail ($level + 1) $maxLevel
+    }
+}
+
 function HandleTemplateDeploymentError($templateValidationResult) {
     Write-Warning "Deployment template validation failed"
 
@@ -357,14 +387,10 @@ function HandleTemplateDeploymentError($templateValidationResult) {
         return
     }
 
-    # Retrieve one or more messages then decode the strings for readability (remove quote escapes, fix link readability, etc.)
-    $parsedMessage = ($templateValidationResult.Details.Message -join "$([System.Environment]::NewLine)$([System.Environment]::NewLine)")
-    $parsedMessage = [System.Net.WebUtility]::UrlDecode($parsedMessage)
-
     Write-Warning "#####################################################"
     Write-Warning "######### TEMPLATE VALIDATION ERROR DETAILS #########"
     Write-Warning "#####################################################"
-    Write-Host $parsedMessage
+    Write-PSResourceManagerError $templateValidationResult 0 5
     Write-Warning "#####################################################"
 }